A stent is a generally cylindrical prosthesis introduced into a lumen of a body vessel via a catheterization technique. Stents may be self-expanding or balloon expandable. Balloon-expandable stents are typically crimped from an initial large diameter to a smaller diameter prior to advancement to a treatment site in the body. Before crimping, a balloon expandable stent is typically placed over an expandable balloon on a catheter shaft. In cases where the stent was manufactured in its fully crimped diameter, the stent is expanded and then crimped on the balloon. To ensure safety, the crimping process should be performed in a sterile environment. Over the years, attempts have been made to crimp the stent on a balloon during the operation in the sterile field. However, most stents are now “pre-crimped” on a suitable balloon in the factory and then delivered to the physician ready for use.
One example of a crimping device for stents based on movable jaws is disclosed in U.S. Pat. No. 6,360,577 to Austin. This crimping device uses sloped planes which force jaws to move from an open position to a closed position. One primary shortcoming is that the length of the sloped plane is given by a whole circle (360°) divided by the number of activated jaws. A long-sloped plane is preferable to reduce circumferential resistance or friction forces, but in order to achieve a smooth aperture for crimping the stent a large number of jaws is needed, which means a shorter sloped plane, less leverage and higher frictional forces. Therefore, the effectiveness of this type of device is substantially limited and may only be practical for stents which have a diameter of 1.5 to 4.0 mm in their expanded size.
In recent years, a variety of prosthetic valves have been developed wherein a valve structure is mounted on a stent and then delivered to a treatment site via a percutaneous catheterization technique. Prosthetic valves are typically much larger in diameter relative to coronary stents. While a typical expanded coronary stent diameter is only 1.5 to 4.0 mm, a stented prosthetic valve diameter will typically be in the range of about 19 to 29 mm, at least 5 times larger.
In another difference, coronary stents are stand-alone metallic devices which may be crimped over a balloon prior to packaging. For prosthetic valves, the stent functions as a scaffold to hold a valve structure which is typically made of biological materials such as pericardium valves or harvested valves. For improved function after deployment, it is often desirable to package such valves in the open (i.e., expanded) state in a preserving solution. Consequently, it is necessary to crimp the valve in the operation room a few minutes before implantation, therefore precluding pre-crimping by the manufacturer over a balloon.
Due to the unique crimping requirements for stent-based prosthetic valves, it has been found that existing crimping devices configured for use with coronary stents are not suitable for use stent-based prosthetic valves. In addition, as discussed above, existing crimping mechanisms suffer from a variety of shortcomings which limit their ability to be adapted for use with stent-based prosthetic valves. Due to the deficiencies associated with existing crimping technology, a new crimping device was described in co-owned U.S. Pat. No. 6,730,118 to Spenser, et al. and relates to a crimping device that is adapted to crimp a prosthetic valve as part of the implantation procedure.
Another version of a prosthetic heart valve crimper is marketed by Machine Solutions Inc. of Flagstaff, Ariz. The HV200 is a disposable crimper that uses multiple pivoting segments to crimp percutaneous heart valves. The Machine Solutions crimpers are also disclosed in U.S. Pat. Nos. 6,629,350 and 6,925,847, both to Motsenbocker. These crimping devices are based on segments which rotate about pivot pins to create radial compression. Unfortunately, the pivoting design tends to concentrate stress in certain areas of the individual segments, and in the mechanism for pivoting them. Also, the user must apply significant force to close the crimper aperture around a relatively large percutaneous heart valve.
U.S. Pat. No. 7,530,253 discloses a crimping mechanism for prosthetic heart valves having linearly moving jaws which has the capacity to crimp a relatively large size valve down to a small delivery size, but is also relatively large in size.
Although the heart valve crimping technology available to date provides an improvement over the existing stent crimper technology, it has been found that a need still exists for a more effective device. It is desirable that such a device be capable of crimping a valve from a diameter of about 29 mm to a crimped size of about 6 mm without requiring excessive force and without inducing high mechanical stresses within the device. It is also desirable that such a device is simple to use and relatively inexpensive to manufacture. It is also desirable that such a device be sterile and suitable for manual operation in a catheter lab or operating room. The present invention addresses this need.